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Full text of "Text Book Of Mechanical Engineering"

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552

Electric Formula.

and motor, the resistance of the circuit causing dissipation of
energy as heat.    If

C = current in amperes,                Q = quantity in Coulombs,

E  electromotive force in volts,    W = work in foot pds.,
R = resistance in Ohms,

Then:

H.P =

c^j^
"746"

EC

746

746 R

v   -      R    -'
 EPR
		v       R              E 746 H. P.          /Hp-.-76-p        w
	
*-i-
o        w
		C          -VH.P.746R     .73?Q 746 H. P.              E2
	
		C2              746 H. P.
	

If 7 be the length of a circuit in feet, both lead and return,
and a  sectional area of wire in sq. in.,

R at 60

8-4

a      1,000,000

when copper wire is used. Also if the E. M. F. drops from E to
e and the current from C to c in flowing from generator to
motor, and if W is the work put in by generator and w that
received by motor,

Efficiency of circuit =-- = - = -

Example 54.A dynamo driven by turbine can generate 50
amperes at 300 volts. The current is carried by two Np. 6 W* G.
copper wires to drive a workshop motor \ mile away. Assuming the
commercial efficiency of the generator as 86%, and that of the motor
as 84/0, find the mechanical efficiency of the whole system*